1. Field of the Invention
The present invention relates to an image recording apparatus used for a recorder of a facsimile apparatus or an output terminal.
2. Related Background Art
A facsimile apparatus generally has a reception buffer for temporarily storing a received image signal. For example, in an ECM (Error Correction Mode) receive mode, when the data amount of received image signal stored in the reception buffer reaches a predetermined data amount (64 Kbytes) (to be referred to as one block hereinafter), image data corresponding to the received image signal of one block is printed on recording paper. For this reason, during reception of a one-block image, printing is kept stopped, and the temperature of heating resistors (thermal head) is excessively reduced. The temperature of the heating resistors does not reach a predetermined temperature at the start of block printing, and the recording density is reduced. Thus, white stripes are formed on the recorded image, resulting in inconvenience.
In a facsimile apparatus, a paper feed motor such as a stepping motor is rotated and driven to move recording paper to relatively change the positional relationship between the recording paper and the heating resistors of the thermal head. Strobed pulses are output to the heating resistors to record an image on the recording paper. During the movement of the recording paper upon rotation and driving of the stepping motor or the like, a convey drive system of the recording paper vibrates to cause an error in the relative positional relationship between the recording paper and the heating resistors. As a result, image quality is greatly degraded.
In particular, in a facsimile apparatus for recording one-block image data when the amount of received image data stored in the reception buffer reaches a predetermined data amount (one block) in the ECM receive mode, after the last line of one block is recorded, the convey drive system greatly vibrates upon stopping of the conveyance of the recording paper. For this reason, in the conventional facsimile apparatus, after the strobed pulse signal to the heating resistors for recording the last line of one block is disabled, the recording paper feed motor continues to vibrate to excessively feed the recording paper. A white stripe is then formed in the corresponding portion of the recorded image, resulting in inconvenience.
In order to eliminate this inconvenience, small pulses are continuously supplied (multi-scan) to the heating resistors not to cause color development of the recording paper during a printing time interval between the blocks to prevent an excessive decrease in temperature of the heating resistors. According to this method, however, the excessive decrease in temperature of the heating resistors between the blocks cannot be perfectly prevented, and white stripes cannot be perfectly eliminated from the printed image. In particular, such a white stripe becomes conspicuous in a halftone image, thereby degrading the quality of the printed image.
In a facsimile apparatus having a recording means of a thermal type, a multi-scan operation can be performed to improve the recording image quality. The multi-scan operation is to increase the number of strobed pulses supplied to a heater for recording an image when a time interval between the recording cycles of the image data is increased, thereby maintaining the heater temperature constant. This operation is effective when the data transmission rate changes and the time interval between the recording periods cannot be maintained constant as in a facsimile apparatus. According to a conventional multi-scan scheme, the maximum value of the multi-scan count is fixed to a predetermined value.
In a normal facsimile apparatus, the recording time interval changes depending on the facsimile communication transmission rate. That is, the recording time interval is prolonged when the transmission rate is low. However, the recording time interval is shortened when the transmission rate is high. On the other hand, since the maximum value of the multi-scan count is predetermined, the temperature of the printing heater tends to be lowered when the transmission rate is low. For this reason, the printing density tends to decrease as a whole, and characters tend to be blurred, thereby causing degradation of image quality. To the contrary, when the transmission rate is high, the temperature of the heater tends to be high. In this case, the printing density tends to be high as a whole, and characters tend to be connected to cause degradation of the image quality.
A normal facsimile apparatus comprises a modem. A coded signal is sent on a transmission line, and this coded signal is received at a receiving end. The receiving end decodes the coded signal. Upon completion of decoding, an image recorder in the receiving end sequentially records the transmitted data. However, since the compression rate of the coded data varies depending on coding schemes, the decoding time varies accordingly. Therefore, the recording time interval varies depending on the coding schemes.
In addition, in a facsimile apparatus having both G2 and G3 modes, the recording time intervals in the G2 and G3 modes are different from each other.
In a facsimile apparatus having an image memory, the recording time interval required for storing data in the image memory and recording the data is different from that required for recording the data without storage.
Various factors which change the recording time intervals are present. Since the multi-scan count or the maximum value of the multi-scan operation is predetermined, the multi-scan for maintaining the heater temperature constant cannot properly function to cause image quality degradation of the recorded image.